Unfortunately I just realize that although the module can be imported and the classifier seems to be compiled, when trying to classify new instances it throws a "Segmentation Fault". This has started happening after I was forced to reinstall orange, on an updated Ubuntu 12.04 . I had no problem training C4.5 before the upgrade. Do you have any idea why this may be hapenning?

I added the -fPIC flag to the compile command, and changed the links in the documentation to point to the latest versions of the files (this might take some time to propagate to the online reference documentation).

But I can't reproduce the segmentation fault. Can you provide a more detailed example?